1. Field of the Invention
The present invention relates to an image processing apparatus suitable for making a hard copy based on an input image signal.
2. Description of the Prior Art
FIG. 1 is a block diagram of a prior art video printer, to which the input signal may be either an NTSC signal or R.multidot.G.multidot.B-SYNC signals. R, G and B digital signals which are A/D converted in a television signal processor 1 are supplied to an image processor 2. The image processor 2 carries out RGB-CMY conversion, masking and undercolor elimination to produce C, M, Y and BK color data. The color data are then supplied to a head driver 3 which drives ink jet heads 4Y, 4M, 4C and 4BK to record an image.
The print heads 4 are moved left and right in a main scan direction by a carriage motor 9 and a paper is fed in a line feed direction by a paper feed motor 7 for each print line.
In this video printer, when a cut sheet is used, it is necessary to set the paper at a record position before the print operation is started. A timing chart therefor is shown in FIG. 2. Assuming that 1,400 pulses are required to feed out the paper from a paper cassette and feed the paper to the predetermined record position by the paper feed motor 7 and an upper limit of a drive frequency of the paper feed motor (pulse motor) is 5 ms, 7 seconds (=1,400 pulses.times.5 ms) are required to set the paper.
In a full-color video printer, it is required to produce an optimum image in accordance with the characteristics of a specific image, and an image having a high tonality is particularly required. Accordingly, normalization is usually effected in order to expand a tonality range for the input video signal. In the normalization, lower and upper limits for the input level of the input video signal are set. It is rare that the input video signal is uniformly distributed over the entire range of density, and it is usually distributed non-uniformly in a high or low density area. It is, therefore, necessary to set the lower and upper limits in accordance with the input video signal. However, since manual adjustment is governed by feeling and experience of an operator, it is difficult to attain an optimum adjustment. Manual adjustment is difficult to attain not only for setting of the upper and lower limits but also for gamma conversion characteristics. In order to attain automatic adjustment, it is necessary to sample a number of points on the input video signal to make a histogram of input video signal levels and set the upper and lower limits based on the overall histogram. The histogram processing may be done for the entire screen. When the screen comprises 480 vertical dots.times.640 horizontal dots, the sample points may be at every tenth horizontal dot line. The image signal of the histogram is usually produced based on a luminance level (Y=0.59G+0.30R+0.11B) but there is no essential difference even if it is produced based on only G. Histograms of G signal data at every tenth dot line are produced. A timing chart therefor is shown in FIG. 3. Assuming that a start signal for one line of A/D conversion is supplied to the television signal processor and signals are sampled vertically, the A/D conversion is completed in 1/60 sec.times.3=1/20 sec at maximum and 1/60 sec.times.2=1/30 sec at minimum. One line (480 vertical dots) of A/D converted data have been stored in a line memory (not shown). The image data is read into the system controller (CPU) 5 which produces the histogram. Assuming that the time required for this processing is 50 ms at maximum, 60 lines.times.(50+50)=6,000 ms or 6 seconds, at maximum, are required in total.
The setting of the record medium to the record position and the setting of parameters for processing the video signal are essential prior to the initiation of recording, and if they are performed sequentially, 7+6=13 seconds are required. Thus, a long recording time is required.